It's not hard to see why the Democratic leadership is optimistic. Republicans must defend 21 of the 33 Senate seats up next year. Perhaps the single biggest predictor of which party will lose Senate seats is exposure: The party with more seats to defend is the one more likely to lose ground.
This is worth remembering in a cycle in which the numbers are so lopsided. That said, there are degrees of exposure. Such factors as retirements, incumbent vulnerability, and the voting patterns of individual states also carry a great deal of weight.
Nearly every Democratic senator up for re-election in 2008 has indicated that he or she intends to run. The exception is Tim Johnson of South Dakota, who had brain surgery in mid-December. Doctors expect that it will be months before Johnson is ready to resume his Senate duties. And he is unlikely to decide before then whether he'll seek a third term.
On the Republican side, Sen. Wayne Allard of Colorado announced on Monday that he will keep his pledge to serve only two terms and will step down at the end of this Congress. Sen. John Warner of Virginia, who will turn 80 next month, is thought to be seriously contemplating retirement; his age and Virginia's changing demographics appear to be major considerations. While Sens. Pete Domenici of New Mexico, who is 74, and Thad Cochran of Mississippi, 69, have said that they will run again, their ages put both on the watch list until they file for re-election. The same is true for Sen. Elizabeth Dole of North Carolina, 70, the subject of frequent retirement rumors.
The newly open seat in Colorado represents the GOP's biggest vulnerability, but several incumbents from both parties are likely to face difficult races.
One measure of potential vulnerability is state voting patterns -- the red state/blue state divide. On the Republican side, Sen. Susan Collins of Maine is from the bluest state: Democratic presidential nominee John Kerry carried Maine by 9 points in 2004. Kerry won Sen. Gordon Smith's Oregon by 4 points, Sen. Norm Coleman's Minnesota by 3 points, and Sen. John Sununu's New Hampshire by 1 point.
Among the Democrats, five incumbents are in solidly red states that President Bush won by at least 9 points: South Dakota's Johnson (22 points), Sen. Max Baucus of Montana (20 points), Sen. Mary Landrieu of Louisiana (15 points), Sen. Jay Rockefeller IV of West Virginia (13 points), and Sen. Mark Pryor of Arkansas (9 points).
Historical voting patterns are far from perfect indicators of future outcomes, but they aren't a bad place to start in assessing the Senate's 2008 contests early in the cycle. Yet the level of vulnerability of individual senators remains the most important factor in determining the overall competitiveness of the Senate playing field.
The most vulnerable Democratic incumbent is Louisiana's Landrieu. She won narrowly in 1996 and 2002 against underwhelming rivals. Since then, Hurricane Katrina has transformed Louisiana's demographics in ways that aren't helpful to Landrieu. Other Democratic incumbents worth keeping an eye on are Baucus, Tom Harkin of Iowa, Pryor, and, of course, Johnson.
In addition to the open seat in Colorado, other potential trouble spots for Republicans seem to be Maine (Collins), Minnesota (Coleman), and New Hampshire (Sununu).
In surveying the lists of vulnerable or potentially vulnerable incumbents and of possible retirements, the pickings for both parties appear pretty slim. Neither seems likely to gain a lot of seats. Still, in early 2005, only four Senate seats were considered extremely competitive. That number grew to nine, and six Republican incumbents ended up losing.
It is difficult to image a worse political environment for Republicans than 2006's was. But the 2008 presidential race will add a degree of uncertainty for both parties, at least until they select their standard-bearers. Until then, let the Senate recruiting begin in earnest.
Associate Editor Jennifer E. Duffy contributed to this report.